This invention relates generally to a selectively operative relief valve useful in significantly reducing tire pressure in order to reduce the overall height of a vehicle and, more particularly, to such a valve employed as part of a central tire inflation system (CTI system or CTIS).
It is often desirable to reduce the overall height of a vehicle for transport. One way to accomplish this is to remove air from the vehicle tires in order to decrease the tire profile and thereby the overall vehicle height. While a tire pressure relief valve directed toward this purpose has heretofore been disclosed in U.S. Pat. No. 5,281,471 entitled "Pressure Relief Valve", incorporated herein by reference, this valve facilitates tire deflation to only a single predetermined tire pressure. The present invention provides an improvement over this previous valve in that it is a two stage valve, allowing deflation to either of two predetermined tire pressures. This feature is particularly useful in allowing vehicle height to remain consistent regardless of whether or not the vehicle is carrying a load. The valve design further allows for adjustment of the higher pressure setting in the assembled valve, thereby reducing the accuracy required in individual valve components as well as making the valve adaptable to varying load weights.
Like the previous valve, the two stage kneeling valve of the present invention is particularly adapted for use in conjunction with a central tire inflation system, such as those disclosed in U.S. Pat. Nos. 4,640,331; 4,878,017; 4,754,792; 4,782,879; 4,804,027; 4,883,106; 4,898,216; 4,922,948; 4,924,928; and published European Patent Applications 0,297,837; 0,352,921; and U.S. patent application Ser. Nos. 726,087 filed Jul. 5, 1991, and 753,562 filed Sep. 3, 1991, and 792,552 filed Nov. 15, 1991, the disclosures of which are incorporated herein by reference. Each of these systems allow a vehicle operator to remotely control the air pressure in vehicle tires. The present valve allows tire deflation to pressures below the preprogrammed pressure limits of the CTIS.
In addition to use in conjunction with such a CTI system, the present valve is equally well suited for use in an inflation only tire pressure maintenance system (TPMS) in order to provide an inexpensive manually controllable deflation capability. The resulting system could be configured to allow three tire pressure settings (such as highway, off-highway and extreme condition settings) and would be operable in a fashion analogous to manually actuatable front hubs on a four-wheel drive system.
The valve includes a body fluidly coupled between a source of pressurized fluid, an inflatable volume such as a tire and the atmosphere. A first valve member is disposed in the body and movable between open and closed positions. In a closed position air is allowed to flow between the pressurized fluid source and the inflatable tire volume so as to allow further inflation or deflation. In the open position a passageway is created between the inflatable volume and the atmosphere in order to effect venting of air from the tire to lower tire pressure to one of two predefined levels. A first pressure level is controlled by a first biasing means which permits venting only until tire pressure is no longer above that necessary to overcome the biasing force.
A second predetermined pressure level is also effected with a second biasing means acting in cooperation with the first biasing means. The first and second biasing means provide venting only until pressure exerted thereby exceeds tire pressure, this second pressure being higher than that effected by the first biasing means acting alone.
The selectively operative relief valve disclosed hereinafter may thus be employed to reduce tire pressure to one of two predetermined pressure levels, in vehicles with or without CTI systems, in order to thereby reduce overall vehicle height and/or improve mobility. These and other advantages of the present invention will become apparent upon review of the following description taken in conjunction with the accompanying drawings.